Method of scrambling reference signals, device and user equipment using the method

ABSTRACT

A Method of scrambling reference signals, device and user equipment using the method are provided. In the method, a plurality of layers of reference signals assigned on predetermined radio resource of a plurality of layers of resource blocks with the same time and frequency resources are scrambled, the method comprising: an orthogonalizing step of multiplying each layer of reference signal selectively by one of a plurality of orthogonal cover codes (OCCs) with the same length wherein the OCC multiplied to a first layer of reference signal can be configured as different from those multiplied to other layers of reference signals; and a scrambling step of multiplying all of symbols obtained from the OCC multiplied to each of the other layers of reference signals by a symbol-common scrambling sequence wherein the symbol-common scrambling sequences can be different from each other for reference signals multiplied by the same OCC.

BACKGROUND Technical Field

The present disclosure relates to the field of signals multiplexingmethod and reference signal design in communication system.

Description of the Related Art

The cooperation between base stations is an important means to mitigateinter-cell-interference in cellular systems and is being intensivelydiscussed in the fourth generation of wireless communication systemstandardizations. It is important for the specifications to enableflexible CoMP (Coordinate Multiple Points) operations, such as JT (jointtransmission), coordinated beamforming, and dynamic point selection,etc.

It is noted that different CoMP operations require different CQI(Channel Quality Indicator) calculation assumptions. For example, for JTtransmission, a UE (user equipment) would assume the signal power isfrom multiple cells (transmission points) that transmit PDSCHs (PhysicalDownlink Shared Channels) to the UE, while other cells are interferingcells. But, for CB (coordinated beamforming) transmission, the UE wouldassume the signal power is from only one cell, while other cells areinterfering cells. In general, the signal power can be measured based onCSI-RSs (Channel Status Information Reference Signals) fromcorresponding cells, which is similar to current techniques (3GPP(3^(rd) Generation Partnership Project) Rel-8/Rel-10). However, thecurrent technique on interference measurement does not work well,because it can measure only the overall interference power (interferencefrom all cells except the serving cell). In general, in Rel-11 andafter, it would preferred to be able to measure interference from eachTP (transmission point) to better cope with flexible CoMP operations.Therefore, a new interference measurement mechanism is required for basestation cooperation.

One method to enable per-TP interference measurement is to have each TPto transmit its own reference signal for the purpose of interferencemeasurement. Those reference signals may be overlapped in time andfrequency domain to enable easy spatial reuse of the time-frequencyresources. To reduce the effort in standardization, it would be anattractive choice to reuse the CSI-RS configuration in Rel-8/Rel-10.

Reusing the CSI-RS configuration includes two folds of meanings: thefirst is to reuse the CSI-RS time and frequency positions, and thesecond is to reuse the CSI-RS OCCs (Orthogonal Cover Codes) andscrambling sequences. To avoid potential impact to legacy UEs, it isstrongly preferred to reuse the CSI-RS time and frequency positions.However, reusing OCCs and scrambling sequences have some drawback inheterogeneous networks, therefore a new OCC and scrambling may befurther investigated. It is noted that the revised OCC and scramblingdoes not reduce legacy UE performance.

The RS (Reference Signal) reusing CSI-RS time and frequency positionsfor interference measurement purposes may be called IM-RS (InterferenceMeasurement Reference Signal). FIG. 1 shows an example of IM-RSconfigurations from different TPs. In FIG. 1 , IM-RSs from threedifferent TPs, i.e., TP1, TP2 and TP3, are transmitted on the same timeand frequency positions (indicated by boxes filled in black in FIG. 1 )by different descrambling. That is, different TPs transmit one portIM-RSs based on the same IM-RS configuration (time and frequencypositions) but scrambled differently. The UE calculates respectiveinterference powers after descrambling.

The problem of the previous OCC and scrambling in a heterogeneousnetwork is as follows. In a heterogeneous network, a UE may beassociated with a TP that has relatively lower receiving power fortraffic offloading purposes. More specifically, a UE may be associatedwith a LPN (Low Power Node) while the receiving power from a macro nodeis much higher than the power from the LPN. In this case, when the UEintends to estimate the interference power from another LPN viadescrambling the related port, the residual interference from the macronode may be much higher than the interference power from the anotherLPN, which implies very inaccurate interference power estimation of theanother LPN. The impact is more severe for subband CQI calculationsbecause of shorter scrambling sequences.

Now, detailed analysis of an exemplary heterogeneous network is givenwith reference to FIG. 2 and FIG. 3 . FIG. 2 shows an example of aheterogeneous deployment, and FIG. 3 shows an example of IM-RSscrambling configuration for the case of FIG. 2 . In FIG. 2 , the UEdesires to receive data from LPN1 functioning as the servingtransmission point while LPN2, LPN3 and macro node are considered asinterfering transmission points. For example, the macro node has atransmitter power of 46 dBm which is much higher than those of LPN1,LPN2 and LPN3. As shown in FIG. 3 , IM-RSs for LPN1, LPN2, LPN3 andmacro node are configured based on the previous OCC and scrambling suchas in Rel-10. Specifically, four layers of IM-RSs are multiplexed on thesame time and frequency resources by two length-2 OCCs [1, 1], [1, −1]and two sets of scrambling sequences [S1, S2], [S3, S4]. That is, themacro node and LPN2 are assigned with the OCC [1, 1] while LPN1 and LPN3are assigned with the OCC [1, −1]. The sequences S1, S2 are respectivelymultiplied to the two symbols of the OCCs for both the macro node andLPN1 while the sequences S3, S4 which are different from the sequencesS1, S2 are respectively multiplied to the two symbols of the OCCs forboth LPN2 and LPN3. Here, the sequences S1 and S2 are independent fromeach other and so do the sequence S3 and S4. In such a case, the CQIcalculation at UE needs to know the interference from each of theinterfering transmission points LPN2, LPN3 and macro node. Taking LPN2as an example, the measured interference from LPN2 is calculated asfollows by the equation (1).

$\begin{matrix}{{\overset{\hat{}}{P}}_{{LPN}2} = {P_{{LPN}2} + {\frac{{s_{3}^{*}s_{1}} + {s_{4}^{*}s_{2}}}{2} \cdot P_{macro}} + {\ldots{\frac{{s_{3}^{*}s_{3}} - {s_{4}^{*}s_{4}}}{2} \cdot P_{{LPN}3}}} + {\frac{{s_{3}^{*}s_{1}} - {s_{4}^{*}s_{2}}}{2} \cdot P_{{LPN}1}}}} & (1)\end{matrix}$

where P_(LPN1) denotes the power the UE receives from LPN1 and thesymbol “*” indicates conjugate.

$\frac{{s_{3}^{*}s_{3}} - {s_{4}^{*}s_{4}}}{2}$

in the equation (1) is zero, but

$\frac{{s_{3}^{\star}s_{1}} - {s_{4}^{\star}s_{2}}}{2}{and}{}\frac{{s_{3}^{\star}s_{1}} + {s_{4}^{\star}s_{2}}}{2}$

are non-zero. Thus, the interference from LPN3 is removed well but thosefrom LPN1 and macro node are remained to impact the measuredinterference from LPN2. Especially, since P_(macro) is much higher thanP_(LPN2), the interference estimation for LPN2 is very inaccurate.

Therefore, how to accurately estimate the interference power from one ormultiple transmission points which may or may not have the strongestreceiving power is required to be solved.

BRIEF SUMMARY

In one aspect of the present disclosure, there is provided a method ofscrambling a plurality of layers of reference signals assigned onpredetermined radio resource of a plurality of layers of resource blockswith the same time and frequency resources, comprising: anorthogonalizing step of multiplying each layer of reference signalselectively by one of a plurality of orthogonal cover codes (OCCs) withthe same length, wherein the OCC multiplied to a first layer ofreference signal can be configured as different from those multiplied toother layers of reference signals; and a scrambling step of multiplyingall of symbols obtained from the OCC multiplied to each of the otherlayers of reference signals by a symbol-common scrambling sequence,wherein the symbol-common scrambling sequences can be different fromeach other for reference signals multiplied by the same OCC.

In another aspect of the present disclosure, there is provided a deviceof scrambling a plurality of layers of reference signals assigned onpredetermined radio resource of a plurality of layers of resource blockswith the same time and frequency resources, comprising: anorthogonalizing unit for multiplying each layer of reference signalselectively by one of a plurality of orthogonal cover codes (OCCs) withthe same length, wherein the OCC multiplied to a first layer ofreference signal can be configured as different from those multiplied toother layers of reference signals; and a scrambling unit for multiplyingall of symbols obtained from the OCC multiplied to each of the otherlayers of reference signals by a symbol-common scrambling sequence,wherein the symbol-common scrambling sequences can be different fromeach other for reference signals multiplied by the same OCC.

In a further aspect of the present disclosure, there is provided a userequipment for receiving from a plurality of transmission points aplurality of layers of reference signals assigned on predetermined radioresources of a plurality of layers of resource blocks with the same timeand frequency resources, comprising: a transceiver unit for receivingthe plurality of layers of resource blocks from the plurality oftransmission points; and a demodulation unit for detecting the pluralityof layers of resource blocks in time domain and/or frequency domain toobtain the plurality of layers of reference signals, wherein, theplurality of layers of reference signals having been subject to thefollowing processes at the plurality of transmission points side: eachlayer of reference signal being multiplied selectively by one of aplurality of orthogonal cover codes (OCCs) with the same length whereinthe OCC multiplied to a first layer of reference signal can beconfigured as different from those multiplied to other layers ofreference signals, and all of symbols obtained from the OCC multipliedto each of the other layers of reference signals being multiplied by asymbol-common scrambling sequence wherein the symbol-common scramblingsequences can be different from each other for reference signalsmultiplied by the same OCC.

In a further aspect of the present disclosure, there is provided amethod of scrambling a plurality of layers of reference signals assignedon predetermined radio resource of a plurality of layers of resourceblocks with the same time and frequency resources, wherein the pluralityof layers of reference signals being grouped into a first set and asecond set, the method comprising: an orthogonalizing step ofmultiplying each layer of reference signal selectively by one of aplurality of orthogonal cover codes (OCCs) with the same length, whereinthe OCCs multiplied to the first set can be configured as different fromthose multiplied to the second set; and a scrambling step of multiplyingall of symbols obtained from the OCC multiplied to each layer ofreference signal by a symbol-common scrambling sequence, wherein thesymbol-common scrambling sequences can be different from each other forreference signals multiplied by the same OCC.

In a further aspect of the present disclosure, there is provided adevice of scrambling a plurality of layers of reference signals assignedon predetermined radio resource of a plurality of layers of resourceblocks with the same time and frequency resources, wherein the pluralityof layers of reference signals being grouped into a first set and asecond set, the device comprising: an orthogonalizing unit formultiplying each layer of reference signal selectively by one of aplurality of orthogonal cover codes (OCCs) with the same length, whereinthe OCCs multiplied to the first set can be configured as different fromthose multiplied to the second set; and a scrambling unit formultiplying all of symbols of obtained from the OCC multiplied to eachlayer of reference signal by a symbol-common scrambling sequence,wherein the symbol-common scrambling sequences can be different fromeach other for reference signals multiplied by the same OCC.

In a further aspect of the present disclosure, there is provided a userequipment for receiving from a plurality of transmission points aplurality of layers of reference signals assigned on predetermined radioresources of a plurality of layers of resource blocks with the same timeand frequency resources, wherein the plurality of layers of referencesignals being grouped into a first set and a second set, the userequipment comprising: a transceiver unit for receiving the plurality oflayers of resource blocks from the plurality of transmission points; anda demodulation unit for detecting the plurality of layers of resourceblocks in time domain and/or frequency domain to obtain the plurality oflayers of reference signals, wherein, the plurality of layers ofreference signals having been subject to the following processes at theplurality of transmission points side: each layer of reference signalbeing multiplied selectively by one of a plurality of orthogonal covercodes (OCCs) with the same length wherein the OCCs multiplied to thefirst set of layers of reference signals can be configured as differentfrom those multiplied to the second set, all of symbols obtained fromthe OCC multiplied to each layer of reference signal being multiplied bya symbol-common scrambling sequence wherein the symbol-common scramblingsequences can be different from each other for reference signalsmultiplied by the same OCC.

In the present disclosure, by the configuration of OCC and scrambling onIM-RSs, IM-RSs from multiple LPNs can be kept fully orthogonal withIM-RS from a macro node and quasi-orthogonal with each other, so that,when detecting the interference from a LPN, the interference from amacro node can be eliminated thoroughly while the interference fromother LPNs can be effectively reduced.

The foregoing is a summary and thus contains, by necessity,simplifications, generalization, and omissions of details; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not intended to be in any way limiting. Otheraspects, features, and advantages of the devices and/or processes and/orother subject matters described herein will become apparent in theteachings set forth herein. The summary is provided to introduce aselection of concepts in a simplified form that are further describedbelow in the Detailed Description. This summary is not intended toidentify key features or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in determining the scopeof the claimed subject matter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. Understanding thatthese drawings depict only several embodiments in accordance with thedisclosure and are, therefore, not to be considered limiting of itsscope, the disclosure will be described with additional specificity anddetail through use of the accompanying drawings, in which:

FIG. 1 shows an example of IM-RS configurations from different TPs;

FIG. 2 shows an example of a heterogeneous deployment;

FIG. 3 shows an example of IM-RS scrambling configuration for the caseof FIG. 2 ;

FIG. 4 shows an example of scrambling configuration for IM-RSs fromdifferent TPs;

FIG. 5 shows an example of scrambling configuration for IM-RSs fromdifferent TPs according to a first embodiment of the present disclosure;

FIG. 6 shows another example of scrambling configuration for IM-RSs fromdifferent TPs according to the first embodiment of the presentdisclosure;

FIG. 7 shows an exemplary communication system according to the firstembodiment of the present disclosure;

FIG. 8 is a block diagram showing a transmission point device accordingto the first embodiment of the present disclosure;

FIG. 9 is a block diagram showing a user equipment (UE) according to thefirst embodiment of the present disclosure;

FIG. 10 shows an example of scrambling configuration for IM-RSs fromdifferent TPs according to a second embodiment of the presentdisclosure;

FIG. 11 shows another example of scrambling configuration for IM-RSsfrom different TPs according to the second embodiment of the presentdisclosure;

FIG. 12 shows an example of scrambling configuration for IM-RSs fromdifferent TPs according to a third embodiment of the present disclosure;

FIG. 13 is a diagram showing a flow chart of a method of scramblingreference signals according to a fifth embodiment of the presentdisclosure; and.

FIG. 14 is a diagram showing a flow chart of a method of scramblingreference signals according to a sixth embodiment of the presentdisclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. It will be readily understood that the aspects ofthe present disclosure can be arranged, substituted, combined, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated and make part of this disclosure.

Based on the detailed analysis with reference to FIGS. 2 and 3 , it isnoted from the equation (1) that the interference from LPN3 iseliminated thoroughly because LPN2 and LPN3 are fully orthogonal witheach other by the orthogonality of OCCs. Also, in the configuration inFIG. 3 , the macro node and LPN1 are orthogonalized by OCCs, which meansthat when detecting the interference from LPN1, the residual power ofthe macro interference can be eliminated very well because of fullorthogonality between them. Specifically, the measured interference fromLPN1 is calculated as follows by the equation (2).

$\begin{matrix}{{\overset{\hat{}}{P}}_{{LPN}1} = {P_{{LPN}1} + {\frac{{s_{1}^{*}s_{1}} - {s_{2}^{*}s_{2}}}{2} \cdot P_{macro}} + {\ldots{\frac{{s_{1}^{*}s_{3}} - {s_{2}^{*}s_{4}}}{2} \cdot P_{{LPN}2}}} + {\frac{{s_{1}^{*}s_{3}} + {s_{2}^{*}s_{4}}}{2} \cdot P_{{LPN}3}}}} & (2)\end{matrix}$

where P_(LPN1) denotes the power the UE receives from LPN1 and thesymbol “*” indicates conjugate.

$\frac{{s_{1}^{\star}s_{1}} - {s_{2}^{\star}s_{2}}}{2}$

in the equation (2) is zero, but

$\frac{{s_{1}^{\star}s_{3}} - {s_{2}^{\star}s_{4}}}{2}{and}{}\frac{{s_{1}^{\star}s_{3}} + {s_{2}^{\star}s_{4}}}{2}$

are non-zero. Thus, the interference from the macro node is removedwell. Therefore, if a macro node and a LPN are CDMed (Code DivisionMultiplexed), it does not need to worry about the macro interferenceafter descrambling.

Accordingly, if all of LPN ports are orthogonal to macro ports, then LPNinterference can be detected with high accuracy. However, current CSI-RSOCC and scrambling design, such as in Rel-10, allows only one LPN portto be orthogonal to the macro port. For example, in FIG. 2 , only LPN1port is orthogonal to the macro port. The feature of the currentscrambling is that it is common for OCCs but specific to OFDM(Orthogonal Frequency Division Multiplexing) symbol, thus the currentscrambling sequence may be called a symbol-specific scrambling sequence.For example, in FIG. 3 , taking the macro node and LPN1 as an example,although they are assigned with different OCCs [1, 1], [1, −1]respectively, they are multiplied with same symbol-specific scramblingsequences S1, S2. Meanwhile, for each of the macro node and LPN1,different OFDM symbols are multiplied by different symbol-specificscrambling sequences, that is, the first symbol of OCC is multipliedwith the symbol-specific scrambling sequence S1 while the second symbolof OCC is multiplied with the symbol-specific scrambling sequence S2which is independent from S1.

A solution to enable multiple LPN ports to be orthogonal to a macro portis to use the scrambling configuration as shown in FIG. 4 . FIG. 4 showsan example of scrambling configuration for IM-RSs from different TPs.For the purpose of simplification, only two LPNs, i.e., LPN1 and LPN2,are shown in FIG. 4 . As compared with FIG. 3 , the configuration forthe macro node and LPN1 is not changed, that is, the macro port and LPN1port are fully orthogonal with each other. Different from FIG. 3 , theLPN2 port in FIG. 4 are configured in the same way with the LPN1 port.Thus, LPN2 port is also fully orthogonal with the macro port.

However, the configuration in FIG. 4 causes severe interference amongLPN ports due to the same OCCs and scrambling configuration. Thus, howto reduce the interference among LPN ports while keeping theorthogonality between all of LPN ports and the macro port is needed tobe considered.

First Embodiment

To reduce the interference among LPN ports, it is proposed to apply anadditional scrambling sequence on each LPN port on the basis of thescrambling configuration for IM-RSs in FIG. 4 . The additionalscrambling sequence may be different for different LPNs to reduce theinterference. Moreover, the additional scrambling sequence has to becommon across the two symbols of OCC to maintain the orthogonality withthe macro port, thus the additional scrambling sequence is called assymbol-common scrambling sequence hereinafter. FIG. 5 shows an exampleof scrambling configuration for IM-RSs from different TPs according tothe first embodiment of the present disclosure. As compared with FIG. 4, the OCC and scrambling for the macro node is unchanged, that is, asingle scrambling is performed on the macro node. On the other hand, forLPNs, on the basis of OCC and scrambling configuration in FIG. 4 , asymbol-common scrambling sequence is further applied to each of LPNs,that is, a double scrambling is performed on each LPN. Specifically, asshown in FIG. 5 , a symbol-common scrambling sequence Q1 is multipliedto two symbols of OOC for LPN1 while another symbol-common scramblingsequence Q2 is multiplied to two symbols of OOC for LPN2.

To sum up, IM-RS configuration includes the following steps:

Firstly, all of LPNs are assigned with a same length-2 OCC which isdifferent from the OCC assigned to a macro node so as to make the macronode and all of LPNs fully orthogonal. Secondly, for each of the macronode and LPNs, the first and the second symbols of OCC are respectivelymultiplied by different symbol-specific scrambling sequences which maybe common to all of the macro node and LPNs. Finally, for each of LPNs,a symbol-common scrambling sequence is multiplied to both the first andthe second symbols of OCC, wherein the symbol-common scrambling sequencemay be different from LPN to LPN.

FIG. 6 shows another example of scrambling configuration for IM-RSs fromdifferent TPs according to the first embodiment of the presentdisclosure. FIG. 6 is to apply the concept in FIG. 5 to the exemplaryheterogeneous network as shown in FIG. 2 , that is, the singlescrambling is applied to the macro node while the double scrambling isapplied to LPN1, LPN2 and LPN3. Specifically, the macro node is assignedwith the OOC [1,1] while LPN1, LPN2 and LPN3 are assigned with the sameOCC [1, −1]. For each of the macro node and three LPNs, two differentsymbol-specific scrambling sequences S1, S2 are respectively multipliedto the first symbol and the second symbol of OCC. Both the first and thesecond symbols of OCC for each of the three LPNs are multiplied with asymbol-common scrambling sequence. The symbol-common scrambling sequenceis Q3, Q4 or Q5 respectively for LPN1, LPN2 or LPN3. Based on the IM-RSconfiguration in FIG. 6 , measured interference from each of the macronode and the three LPNs can be calculated by the following equations.

{circumflex over (P)} _(LPN1) =P _(LPN1)+0·P _(macro) +q* ₃ q ₄ ·P_(LPN2) +q* ₃ q ₅ ·P _(LPN3)  (3)

{circumflex over (P)} _(LPN2) =P _(LPN2)+0·P _(macro) +q* ₄ q ₃ ·P_(LPN1) +q* ₄ q ₅ ·P _(LPN3)  (4)

{circumflex over (P)} _(LPN3) =P _(LPN3)+0·P _(macro) +q* ₅ q ₃ ·P_(LPN1) +q* ₅ q ₄ ·P _(LPN2)  (5)

{circumflex over (P)} _(macro) =P _(macro)+0·P _(LPN1)+0·P _(LPN2)+0·P_(LPN3)+ . . . noisefactors  (6)

From the above equations (3)-(6), since all of LPN ports are fullyorthogonal to the macro port, the interference from the macro node canbe removed well in the equations (3)-(5). Although the interference fromother LPNs is remained in the equation (3)-(5) since the three LPNs arequasi-orthogonal with each other by the symbol-common scramblingsequences, the interference from other LPNs is relatively small so asnot to impact LPN interference estimation very much. Furthermore, forthe estimation of the interference from the macro node, interferencefrom LPNs are all removed thoroughly as shown in the equation (6).

FIG. 7 shows an exemplary communication system 70 according to the firstembodiment of the present disclosure. As shown in FIG. 7 , thecommunication system 70 includes multiple TPs such as TP 800 and a UE900. In the communication system 70, UE 900 may communicate with themultiple TPs such as TP 800. The multiple TPs includes a macro node andmultiple LPNs. The TP 800 may be a macro node or a LPN. For the purposeof CQI calculation at UE 900, all of TPs transmit IM-RSs configured asdescribed above to UE 900. In the following, the detailed configurationof TP 800 and UE 900 will be described with reference to FIGS. 8 and 9 .

FIG. 8 is a block diagram showing a device 8000 according to the firstembodiment of the present disclosure.

The device 8000 according to the first embodiment of the presentdisclosure may be configured in the transmission point 800 forcommunicating with at least one UE (user equipment) such as UE 900 in acommunication system. The device 8000 is capable of scrambling multiplelayers of RS signals assigned on predetermined locations (radioresource, which means the time and/or frequency resource such assub-carrier, sub-frame, etc.) of a plurality of layers of resourceblocks with the same time and frequency resources. As shown in FIG. 8 ,the device 8000 includes: an orthogonalizing unit 8010 which multiplieseach layer of RS signal selectively by one of a first and a secondlength-2 orthogonal cover codes (OCCs) wherein the first OCC ismultiplied to the layer of RS signal transmitted from a macro node whilethe second OCC is multiplied to layers of RS signals transmitted fromLPNs; a scrambling unit 8020 which multiplies the two symbols of the OCCmultiplied to each layer of RS signal respectively by differentsymbol-specific sequences which are common to all layers of RS signalsfrom all of transmission points, and multiplies the two symbols of theOCC multiplied to each of layers of RS signals transmitted from LPNs bya symbol-common scrambling sequence which is different from LPN to LPN;and a transceiver unit 8030 which transmits the plurality of layers ofresource blocks obtained from the scrambling unit 8020 to the at leastone UE. It should be noted that RS signals here can be IM-RS signals.

The transmission point device 8000 according to the present disclosuremay further include a CPU (Central Processing Unit) 8100 for executingrelated programs to process various data and control operations ofrespective units in the transmission point device 8000, a ROM (Read OnlyMemory) 8130 for storing various programs required for performingvarious process and control by the CPU 8100, a RAM (Random AccessMemory) 8150 for storing intermediate data temporarily produced in theprocedure of process and control by the CPU 8100, and/or a storage unit8170 for storing various programs, data and so on. The aboveorthogonalizing unit 8010, scrambling unit 8020, transceiver unit 8030,CPU 8100, ROM 8130, RAM 8150 and/or storage unit 8170 etc. may beinterconnected via data and/or command bus 8200 and transfer signalsbetween one another.

Respective units as described above do not limit the scope of thepresent disclosure. According to one embodiment of the disclosure, thefunction of any of the above orthogonalizing unit 8010, scrambling unit8020, and transceiver unit 8030 may also be implemented by functionalsoftware in combination with the above CPU 8100, ROM 8130, RAM 8150and/or storage unit 8170 etc.

By the orthogonalizing unit 8010 and the scrambling unit 8020 in thedevice 8000, multiple layers of IM-RS signals from a macro node andmultiple LPNs may be configured as shown in FIGS. 5 and 6 . That is,IM-RSs from multiple LPNs are kept fully orthogonal with IM-RS from amacro node and quasi-orthogonal with each other by applying a singlescrambling on a macro node and a double scrambling on each of LPNs, sothat, when detecting the interference from a LPN, the interference froma macro node can be eliminated thoroughly while the interference fromother LPNs can be effectively reduced.

It should be noted that, instead of being in a TP, the device 8000 maybe configured in another node which functions as a central node forscrambling multiple RS signals transmitted from multiple TPs. Also, thedevice 8000 may not include the transceiver unit 8030 when beingconfigured in a TP, instead, transmission of multiple layers of resourceblocks is implemented by a transceiver device in the TP. In addition,symbol-specific scrambling on all of layers of RS signals andsymbol-common scrambling to the layers of RS signals transmitted fromLPNs may be implemented respectively by two separate scrambling units,instead of one scrambling unit 8020.

FIG. 9 is a block diagram showing user equipment (UE) 900 according tothe first embodiment of the present disclosure.

The UE 900 according to the first embodiment of the present disclosureis used for communicating with multiple transmission points including amacro node and multiple LPNs in a communication system. The UE 900receives from the transmission points a plurality of layers of RSsignals assigned on predetermined locations (radio resource, which meansthe time and/or frequency resource such as sub-carrier, sub-frame, etc.)of a plurality of layers of resource blocks with the same time andfrequency resources. As shown in FIG. 9 , the UE 900 includes: atransceiver unit 901 which receives the plurality of layers of resourceblocks; and a demodulation unit 902 which detects the plurality oflayers of resource blocks in time domain and/or frequency domain toobtain the plurality of layers of RS signals, wherein each layer of RSsignal transmitted from each transmission point is multiplied by one ofa first and a second length-2 orthogonal cover codes (OCCs) wherein thefirst OCC is multiplied to the layer of RS signal from the macro nodewhile the second OCC is multiplied to layers of RS signals from themultiple LPNs, the two symbols of the OCC multiplied to each layer of RSsignal transmitted from each transmission point respectively bydifferent symbol-specific sequences which are common to all layers of RSsignals from all of transmission point devices, and the two symbols ofthe OCC multiplied to the layer of RS signal transmitted from each LPNby a symbol-common scrambling sequence which is different from LPN toLPN. It should be noted that RS signals here can be IM-RS signals.

As described previously with reference to FIGS. 5 and 6 , layers ofIM-RS signals received by UE 900 from a macro node and multiple LPNs maybe configured as shown in FIGS. 5 and 6 . That is, IM-RSs from multipleLPNs are kept fully orthogonal with IM-RS from a macro node andquasi-orthogonal with each other by applying a single scrambling on amacro node and a double scrambling on each of LPNs, so that, whendetecting the interference from a LPN at UE 900, the interference from amacro node can be eliminated thoroughly while the interference fromother LPNs can be effectively reduced.

The UE 900 according to the present disclosure may further include a CPU(Central Processing Unit) 910 for executing related programs to processvarious data and control operations of respective units in the UE 900, aROM (Read Only Memory) 913 for storing various programs required forperforming various process and control by the CPU 910, a RAM (RandomAccess Memory) 915 for storing intermediate data temporarily produced inthe procedure of process and control by the CPU 910, and/or a storageunit 917 for storing various programs, data and so on. The abovetransceiver unit 901, demodulation unit 902, CPU 910, ROM 913, RAM 915and/or storage unit 917 etc. may be interconnected via data and/orcommand bus 920 and transfer signals between one another.

Respective units as described above do not limit the scope of thepresent disclosure. According to one embodiment of the disclosure, thefunction of any of the above transceiver unit 901 and demodulation unit902 may also be implemented by functional software in combination withthe above CPU 910, ROM 913, RAM 915 and/or storage unit 917 etc.

According to the present embodiment, by applying a single scrambling ona macro node and a double scrambling on each of LPNs, IM-RSs frommultiple LPNs can be kept fully orthogonal with IM-RS from a macro nodeand quasi-orthogonal with each other, so that, when detecting theinterference from a LPN, the interference from a macro node can beeliminated thoroughly while the interference from other LPNs can beeffectively reduced.

Second Embodiment

In the method of the first embodiment as described above, since a singlescrambling is applied on a macro node and a double scrambling is appliedon each of LPNs, UE needs to distinguish the macro node and LPNs for thepurpose of accurate descrambling. In general, UE does not know which TPis a macro node and which TP is a LPN. Thus, it is preferred to adoptthe same scrambling format for a macro node and a LPN. In the presentembodiment, it is proposed to apply double scrambling on both LPN andmacro node so as to avoid informing UE which transmission point is themacro node.

FIG. 10 shows an example of scrambling configuration for IM-RSs fromdifferent TPs according to the second embodiment of the presentdisclosure. As shown in FIG. 10 , there are configured two sets ofIM-RSs, i.e., IM-RS set 1 and IM-RS set 2. Each IM-RS in the set 1 isassigned with the length-2 OCC [1, 1] while each IM-RS in the set 2 isassigned with the OCC [1, −1]. Thus, by the above OCC configuration,IM-RS ports in the set 1 are fully orthogonal with IM-RS ports in theset 2. Furthermore, for each IM-RS either in the set 1 or in the set 2,the two symbols of OCC are multiplied respectively by two differentsymbol-specific scrambling sequences which are common to all of IM-RSsin the set 1 and the set 2. In addition, in the set 1 or in the set 2,the two symbols of OCC for each IM-RS are further multiplied by asymbol-common scrambling sequence which is different from IM-RS toIM-RS. By such additional configuration, IM-RS ports in both the set 1and the set 2 are applied double scrambling, thereby IM-RS ports in theset 1 are quasi-orthogonal with each other while IM-RS ports in the set2 are quasi-orthogonal with each other.

As for IM-RS configuration for a macro node and LPNs, IM-RSs frommultiple LPNs can be kept fully orthogonal with IM-RS from a macro nodeand quasi-orthogonal with each other as long as IM-RS from the macronode and IM-RSs from the multiple LPNs are configured respectively fromdifferent sets, that is, if the OCC and scrambling configuration ofIM-RS from the macro node is selected from the IM-RS set 1, the OCC andscrambling configuration of IM-RSs from the multiple LPNs should beselected from the IM-RS set 2, and vice versa.

It is noted that, in FIG. 10 , IM-RSs in the set 1 are multipliedrespectively by symbol-common scrambling sequences Q1, Q2 and Q3 whichare different from symbol-common scrambling sequences Q4, Q5 and Q6multiplied respectively to IM-RSs in the set 2. However, the presentdisclosure is not limited to this. FIG. 11 shows another example ofscrambling configuration for IM-RSs from different TPs according to thesecond embodiment of the present disclosure.

In FIG. 11 , the configuration of OCC and symbol-specific scramblingsequence for the set 1 and the set 2 are the same with that in FIG. 10 .Different from FIG. 10 , IM-RSs in the set 1 are multiplied respectivelyby symbol-common scrambling sequences Q1, Q2 and Q3 which are alsomultiplied respectively to IM-RSs in the set 2. Quasi-orthogonalitywithin respective sets or among IM-RS ports assigned with a same OCC canbe obtained as long as IM-RS ports assigned with a same OCC aremultiplied by different symbol-common scrambling sequences. Therefore,the symbol-common scrambling sequence may be reused among differentsets, that is, among OCCs.

According to the present embodiment, the scrambling unit 8020 in thedevice 8000 may further multiplies the two symbols of the OCC multipliedto the layer of RS signal transmitted from the macro node by asymbol-common scrambling sequence which can be the same as one of ordifferent from all of the symbol-common scrambling sequences multipliedto the other layers of RS signals transmitted from LPNs. Alternatively,the device 8000 may include another scrambling unit to implement suchscrambling function.

According to the present embodiment, in addition to the effects achievedin the first embodiment, by applying double scrambling to both a macronode and LPNs, there is no need to inform UE which transmission point isthe macro node.

Third Embodiment

The above two embodiments are both related to length-2 OCCs. However,the present disclosure is not limited to this and may be extended tolength-4 OCCs and so on. As an example, the present embodiment is toapply double scrambling to length-4 OCCs. Note that, 4 port CSI-RS isadopted on two adjacent OFDM symbols and two subcarriers that are sixsubcarriers away on a resource block.

FIG. 12 shows an example of scrambling configuration for IM-RSs fromdifferent TPs according to the third embodiment of the presentdisclosure. FIG. 12 is to extend the concept in the above embodiment toa length-4 OCC case. Specifically, as shown in FIG. 12 , IM-RS from amacro node is assigned with a length-4 OCC [1, 1, 1, 1], IM-RSs fromLPN1 and LPN4 are assigned with a length-4 OCC [1, −1, 1, −1], IM-RSsfrom LPN2 and LPN5 are assigned with a length-4 OCC [1, 1, −1, −1], andIM-RSs from LPN3 and LPN6 are assigned with a length-4 OCC [1, −1, −1,1]. Thus, IM-RSs from LPNs are kept fully orthogonal with IM-RS from themacro node since each of IM-RSs from LPNs is assigned with a differentlength-4 OCC from that for the macro node. Furthermore, for each of themacro node and the six LPNs, four symbols of the assigned length-4 OCCare multiplied respectively by four different symbol-specific scramblingsequences which can be common to all of IM-RSs from the macro node andLPNs. Then, for each of the macro node and the six LPNs, four symbols ofthe assigned length-4 OCC are additionally multiplied by a symbol-commonscrambling sequence. That is, the symbol-common scrambling is common totwo OFDM symbols and two subcarriers that are six carriers away on aresource block. The symbol-common sequence may be common among differentOCCs but should be allowed to be different between LPNs assigned with asame OCC.

Specifically, as shown in FIG. 12 , the macro node and LPN1 to LPN3 aremultiplied by a same symbol-common sequence Q1 since they are assignedwith different OCCs. LPN4 is multiplied by a symbol-common scramblingsequence Q2 different from the symbol-common sequence Q1 multiplied toLPN1 since they are assigned with a same OCC [1, −1, 1, −1]. Also, LPN5is multiplied by a symbol-common scrambling sequence Q2 different fromthe symbol-common sequence Q1 multiplied to LPN2 since they are assignedwith a same OCC [1, 1, −1, −1]. The same is true for LPN3 and LPN6.Similarly, LPN4 to LPN6 are multiplied by a same symbol-common sequenceQ2 since they are assigned with different OCCs. It is noted that, theconfiguration shown in FIG. 12 is only illustrative and the presentdisclosure is not limited to it. Obviously, LPN1 to LPN3 may bemultiplied by the symbol-common sequence Q2 while LPN4 to LPN6 aremultiplied by symbol-common sequence Q1.

In this situation, by using length-4 OCC to the macro node and six LPNs,not only the interference from the macro node but also the interferencefrom some LPNs is eliminated thoroughly. Taking LPN1 as an example, itis interfered by LPN4 only since they are assigned with a same OCC. Bythe application of different symbol-common sequences, the interferencefrom LPN4 can be reduced. On the other hand, since LPN1 is fullyorthogonal with not only the macro node but also LPN2, LPN3, LPN5 andLPN6, the interference from both the macro node and the four LPNs isremoved very well.

It is noted that length-4 OCC is only an example and the length of OCCis not limited to 2 or 4. The present disclosure may be extended to OCCwith an even longer length.

According to the present embodiment, by using length-4 OCC and doublescrambling to both the macro node and LPNs, the interference from otherLPNs are further eliminated.

Fourth Embodiment

In the above embodiments, symbol-specific scrambling sequences arefirstly used to all of the macro node and LPNs and then symbol-commonscrambling sequences are further used to only LPNs or all of the macronode and LPNs. However, the present disclosure is not limited to this.The order of application of symbol-specific scrambling sequences andsymbol-common scrambling sequences is not fixed and may be reversed.That is, symbol-common scrambling sequences may be applied beforesymbol-specific scrambling sequences.

Furthermore, it is also possible to use symbol-common scramblingsequences only without applying symbol-specific scrambling sequences. Byconfiguration of OCC and symbol-specific scrambling sequences only, thepresent disclosure can achieve the same effects as the aboveembodiments. Specifically, the full orthogonality between the macro nodeand LPNs can be obtained by OCC configuration while quasi-orthogonalityamong LPNs can be obtained by symbol-specific scrambling.

According to the present embodiment, the orthogonalizing unit 8010 maymultiply each layer of reference signal selectively by one of aplurality of OCCs with the same length, wherein the OCC multiplied to afirst layer of reference signal transmitted from for example a firsttransmission point can be configured as different from those multipliedto other layers of reference signals transmitted from for example othertransmission points, and the scrambling unit 8020 may multiply all ofsymbols obtained from the OCC multiplied to each of the other layers ofreference signals by a symbol-common scrambling sequence, wherein thesymbol-common scrambling sequences can be different from each other forreference signals multiplied by the same OCC.

In addition, although the present disclosure has been described takingone macro node as an example, the number of macro nodes is not limitedto one and there may be several macro nodes in a communication system.The present disclosure is also applicable to a case in which there aremultiple macro nodes and multiple LPNs. For example, it is only neededto achieve full orthogonality between macro nodes and LPNs by OCCconfiguration and to obtain quasi-orthogonality respectively among macronodes and among LPNs by symbol-common scrambling.

According to the present embodiment, the orthogonalizing unit 8010 maymultiply each layer of reference signal, being grouped into two setswith a first set being transmitted from for example a first group oftransmission points and a second set being transmitted from for examplea second group of transmission points, selectively by one of a pluralityof OCCs with the same length, wherein the OCCs multiplied to the firstset can be configured as different from those multiplied to the secondset, and the scrambling unit 8020 may multiply all of symbols ofobtained from the OCC multiplied to each layer of reference signal by asymbol-common scrambling sequence, wherein the symbol-common scramblingsequences can be different from each other for reference signalsmultiplied by the same OCC.

The following is to realize the idea of the present disclosure in 3GPPspecifications TS 36.211. It is proposed to make some changes to thecurrent specifications as follows. As an example, the followingdefinition of the present embodiment corresponds to the case of thesecond embodiment where no signaling is needed to indicate UE of “macronode” and “LPN” and length-2 OCCs are assumed.

The symbol-specific scrambling sequence r_(l,n) _(s) (m) is defined by

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{m = 0},1,\ldots,{N_{RB}^{\max,{DL}} - 1}} & (7)\end{matrix}$

where n_(s) is the slot number within a radio frame and l is the OFDMsymbol number within the slot. The pseudo-random sequence c(i) isdefined in Section 7.2 of 3GPP TS 36.211 V10.4.0. The pseudo-randomsequence generator shall be initialized with

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(CSIRS)+2·N _(ID) ^(CSIRS)+N _(CP)  (8)

at the start of each OFDM symbol where N_(ID) ^(CSIRS) indicates CSI-RSID and

$N_{CP} = \left\{ \begin{matrix}1 & {{for}{normalCP}} \\0 & {{for}{extendedCP}}\end{matrix} \right.$

The symbol-common scrambling sequence r′_(l,n) _(s) (m) is defined by

$\begin{matrix}{{{r_{l,n_{s}}^{\prime}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{m = 0},1,\ldots,{N_{RB}^{\max,{DL}} - 1}} & (9)\end{matrix}$

where n_(s) is the slot number within a radio frame and l is the OFDMsymbol number within the slot. The pseudo-random sequence c(i) isdefined in Section 7.2 of 3GPP TS 36.211 V10.4.0. The pseudo-randomsequence generator shall be initialized with

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(IMRS)+1)+2·N _(ID) ^(IMRS)+N _(CP)  (10)

at the start of each OFDM symbol where N_(ID) ^(IMRS) indicates IM-RS IDand

$N_{CP} = \left\{ \begin{matrix}1 & {{for}{normalCP}} \\0 & {{for}{extendedCP}}\end{matrix} \right.$

As compared with the definition of CSI reference-signal sequence forexample in section 6.10.5 in 3GPP TS 36.211 V10.4.0, the symbol-specificscrambling sequence r_(l,n) _(s) (m) in the present disclosure is thesame as CSI reference-signal sequence defined in 3GPP TS 36.211. Therandom seed generation equation (8) is the same as that defined in 3GPPTS 36.211 only except that the parameter N_(ID) ^(cell) is replaced byN_(ID) ^(CSIRS). In 3GPP TS 36.211, the random seed for CSIreference-signal sequence is based on cell ID. In the presentdisclosure, N_(ID) ^(CSIRS) is not limited to cell ID and may be otherIDs which may be signaled by the higher layer. For example, returningback to FIGS. 10 and 11 , two different symbol-specific scramblingsequences 51 and S2 are generated from the above equation (7) and (8)and are based on different N_(ID) ^(CSIRS).

In view of generation equation and random seed generation equation, thesymbol-common scrambling sequence r′_(l,n) _(s) (m) defined in thepresent disclosure is similar with the symbol-specific scramblingsequence r_(l,n) _(s) (m), the difference between them is that they arebased on different IDs, that is, the former is based on N_(ID) ^(IMRS)and the latter is based on N_(ID) ^(CSIRS). Taking FIG. 10 and FIG. 11as an example, different symbol-common scrambling sequences Q1-06 aregenerated from the above equation (9) and (10) and are based ondifferent N_(ID) ^(IMRS) which may be also signaled by the higher layer.

The above definition is applicable for both CoMP scenarios 3 and 4.Specifically, for scenario 3, the random seed for the symbol-commonscrambling sequence can be based on cell ID. On the other hand, forscenario 4, the random seed for the symbol-common scrambling sequencecan be based on CSI-RS ID or IM-RS ID signaled by the higher layer. Itis noted that the CSI-RS ID may be also used in CSI-RS scrambling.

In such case, with respect to DL (downlink) signaling, three scramblingrandom seeds and related OCC are signaled or to be specified for eachIM-RS port. Specifically, two different random seeds are for twosymbol-specific scrambling sequences for different OFDM symbols, anotherrandom seed is for the symbol-common scrambling sequence which is commonacross OFDM symbols, and one bit is for the OCC.

According to the present embodiment, in subframes configured for IM-RStransmission, the symbol-specific scrambling sequence r_(l,n) _(s) (m)and the symbol-common scrambling sequence r′_(n) (in) shall be mapped tocomplex-valued modulation symbols a_(k,l) ^((p)) used as referencesymbols on antenna port p according to

$\begin{matrix}{a_{k,l}^{(p)} = {w_{l^{''}} \cdot {r_{l,n_{s}}\left( m^{\prime} \right)} \cdot {r_{l^{\prime},n_{s}}^{\prime}\left( m^{\prime} \right)}}} & (11)\end{matrix}$ where $k = {k^{\prime} + {12m} + \left\{ \begin{matrix}{{{{- 0}{for}p} \in \left\{ {{15},{16}} \right\}},{{normal}{cyclic}{prefix}}} \\{{{{- 6}{for}p} \in \left\{ {{17},{18}} \right\}},{{normal}{cyclic}{prefix}}} \\{{{{- 1}{for}p} \in \left\{ {{19},{20}} \right\}},{{normal}{cyclic}{prefix}}} \\{{{{- 7}{for}p} \in \left\{ {{21},{22}} \right\}},{{normal}{cyclic}{prefix}}} \\{{{{- 0}{for}p} \in \left\{ {{15},{16}} \right\}},{{extended}{cyclic}{prefix}}} \\{{{{- 3}{for}p} \in \left\{ {{17},{18}} \right\}},{{extended}{cyclic}{prefix}}} \\{{{{- 6}{for}p} \in \left\{ {{19},{20}} \right\}},{{extended}{cyclic}{prefix}}} \\{{{{- 9}{for}p} \in \left\{ {{21},{22}} \right\}},{{extended}{cyclic}{prefix}}}\end{matrix} \right.}$ $l = {l^{\prime} + \left\{ \begin{matrix}l^{''} & {{{{CSI}{referencesignal}{configurations}0} - 19},{{normal}{cyclic}{prefix}}} \\{2l^{''}} & {{{{CSI}{referencesignal}{configurations}20} - 31},{{normal}{cyclic}{prefix}}} \\l^{''} & {{{{CSI}{referencesignal}{configurations}0} - 27},{{extended}{cyclic}{prefix}}}\end{matrix} \right.}$ $w_{l^{''}} = \left\{ \begin{matrix}1 & {{{if}{{mod}\left( {N_{D}^{IMRS},2} \right)}} = 0} \\\left( {- 1} \right)^{l^{''}} & {{{if}{{mod}\left( {N_{D}^{IMRS},2} \right)}} = 1}\end{matrix} \right.$ l^(″) = 0, 1 m = 0, 1, …, N_(RB)^(DL) − 1$m^{\prime} = {m + \left\lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \right\rfloor}$

and the quantity (k′,l′) and the necessary conditions on n_(s) are givenby Tables 6.10.5.2-1 and 6.10.5.2-2 in 3GPP TS 36.211 V10.4.0 for normaland extended cyclic prefix respectively.

The difference of the equation (11) from that in 3GPP TS 36.211 is theadditional multiplication by r′_(l′,n) _(s) (m′) in which the subscriptl′ is to have the symbol-common scrambling sequence. The definition ofparameters k, l, 1″, in and m′ are the same as those in 3GPP TS 36.211while the parameter w_(l″) is different. The parameter w_(l″) indicatesthat the OCC is based on N_(ID) ^(IMRS) in the present embodiment.However, it is only one possible design and OCC may be configured by thehigher layer. In addition, for the parameter k, the designation ofantenna port p, such as 15, 16, 17, 18, 19, 20, 21, 22, may be changedif a new port needs to be defined as required by the communicationsystem.

CSI-RS defined in Rel-10 is for channel estimation rather thaninterference. Instead of defining additional pilots dedicated forinterference measurement, the present disclosure can reuse one or moreof the CSI-RS configurations for this purpose with minor modifications,for example based on the above definition. For example, in Rel-10,support of up to 40 CSI-RS ports is possible (normal CP (cyclic prefix),2Tx (transmitter)) by the exhaustive list of CSI-RS port combinations.In a single cell transmission, only up to 8 CSI-RS ports are needed tosupport 8 Tx antennas and the rest is to support additional reuse ifneeded.

It is noted that, when only symbol-common scrambling is performed asdescribed in the fourth embodiment, the equation (11) can be simplifiedas

a _(k,l) ^((p)) =w _(l″) ·r′ _(l′,n) _(s) (m′)  (12)

According to the present embodiment, based on the minor modification to3GPP specifications TS 36.211, the interference measurement mechanism ofthe present disclosure is easy to implement.

Fifth Embodiment

FIG. 13 is a diagram showing a flow chart of a method of scramblingreference signals according to the fifth embodiment of the presentdisclosure.

As shown in FIG. 13 , the method 1300 according to the fifth embodimentof the present disclosure is used for scrambling a plurality of layersof reference signals assigned on predetermined radio resource of aplurality of layers of resource blocks with the same time and frequencyresources, wherein a first layer of reference signal may be for exampletransmitted from a first transmission point and other layers may be forexample transmitted from other transmission points. In the step 1301,each layer of reference signal is multiplied selectively by one of aplurality of orthogonal cover codes (OCCs) with the same length, whereinthe OCC multiplied to the first layer of reference signal can beconfigured as different from those multiplied to the other layers ofreference signals. In the step 1302, all of symbols obtained from theOCC multiplied to each of the other layers of reference signals aremultiplied by a symbol-common scrambling sequence, wherein thesymbol-common scrambling sequences can be different from each other forreference signals multiplied by the same OCC.

According to the present embodiment, the above step S1301 can beexecuted by the orthogonalizing unit 8010, and the above steps S1302 canbe executed by the scrambling unit 8020.

According to the present embodiment, the symbol-common scramblingsequence is expressed as r′_(l,n) _(s) (in) which is defined by theequation (9) and its pseudo-random sequence generator is initializedwith the equation (10) at the start of each OFDM symbol.

According to the present embodiment, the symbol-common scramblingsequence r′_(l′,n) _(s) (m) is mapped to complex-valued modulationsymbols a_(k,l) ^((p)) used as reference symbols on antenna port paccording to the equation (12).

According to the present embodiment, although not shown in FIG. 13 , themethod 1300 may further include a second scrambling step of multiplyingall of symbols obtained from the OCC multiplied to each layer ofreference signal respectively by different symbol-specific scramblingsequences which can be configured as common to all of the plurality oflayers of reference signals. This step may also be executed by thescrambling unit 8020 or may be executed by another scrambling unit (notshown in FIG. 8 ) in the device 8000.

According to the present embodiment, the symbol-specific scramblingsequence is expressed as r_(l,n) _(s) (m) which is defined by theequation (7) and its pseudo-random sequence generator is initializedwith the equation (8) at the start of each OFDM symbol.

According to the present embodiment, the symbol-specific scramblingsequence r_(l,n) _(s) (m) and the symbol-common scrambling sequencer′_(l′,n) _(s) (m) are mapped to complex-valued modulation symbolsa_(k,l) ^((p)) used as reference symbols on antenna port p according tothe equation (11).

According to the present embodiment, although not shown in FIG. 13 , themethod 1300 may further include a third scrambling step of multiplyingall of symbols obtained from the OCC multiplied to the first layer ofreference signal by another symbol-common scrambling sequence which isthe same as one of or different from all of the symbol-common scramblingsequences multiplied to the other layers of reference signals. This stepmay also be executed by the scrambling unit 8020 or may be executed by afurther scrambling unit (not shown in FIG. 8 ) in the device 8000.

According to the present embodiment, the random seeds for thesymbol-common sequences are based on cell ID or CSI-RS ID or IM-RS ID.

According to the present embodiment, random seeds for thesymbol-specific sequences and the symbol-common sequences and the OCCsare signaled to user equipment or to be specified for each port.

According to the present embodiment, the reference signals areinterference measurement reference signals.

According to the present embodiment, by the configuration of OCC andscrambling on IM-RSs, IM-RSs from multiple LPNs are kept fullyorthogonal with IM-RS from a macro node and quasi-orthogonal with eachother, so that, when detecting the interference from a LPN, theinterference from a macro node can be eliminated thoroughly while theinterference from other LPNs can be effectively reduced.

Sixth Embodiment

FIG. 14 is a diagram showing a flow chart of a method of scramblingreference signals according to the sixth embodiment of the presentdisclosure.

As shown in FIG. 14 , the method 1400 according to the presentembodiment is used for scrambling a plurality of layers of referencesignals assigned on predetermined radio resource of a plurality oflayers of resource blocks with the same time and frequency resources,wherein the plurality of layers of reference signals may be grouped intotwo sets in which a first set may be for example transmitted from afirst group of transmission points and a second set may be for exampletransmitted from a second group of transmission points. In the stepS1401, each layer of reference signal is multiplied selectively by oneof a plurality of orthogonal cover codes (OCCs) with the same length,wherein the OCCs multiplied to the first set can be configured asdifferent from those multiplied to the second set. In the step S1402,all of symbols obtained from the OCC multiplied to each layer ofreference signal are multiplied by a symbol-common scrambling sequence,wherein the symbol-common scrambling sequences can be different fromeach other for reference signals multiplied by the same OCC.

According to the present embodiment, the above step S1401 can beexecuted by the orthogonalizing unit 8010, and the above steps S1402 canbe executed by the scrambling unit 8020.

According to the present embodiment, the symbol-common scramblingsequence is expressed as r′_(l,n) _(s) (in) which is defined by theequation (9) and its pseudo-random sequence generator is initializedwith the equation (10) at the start of each OFDM symbol.

According to the present embodiment, the symbol-common scramblingsequence r′_(l′″,n) _(s) (m) is mapped to complex-valued modulationsymbols a_(k,l) ^((p)) used as reference symbols on antenna port paccording to the equation (12).

According to the present embodiment, although not shown in FIG. 14 , themethod 1400 may further include a second scrambling step of multiplyingall of symbols obtained from the OCC multiplied to each layer ofreference signal respectively by different symbol-specific scramblingsequences which can be configured as common to all of the plurality oflayers of reference signals. This step may also be executed by thescrambling unit 8020 or may be executed by another scrambling unit (notshown in FIG. 8 ) in the device 8000.

According to the present embodiment, the symbol-specific scramblingsequence is expressed as r_(l,n) _(s) (m) which is defined by theequation (7) and its pseudo-random sequence generator is initializedwith the equation (8) at the start of each OFDM symbol.

According to the present embodiment, the symbol-specific scramblingsequence r_(l,n) _(s) (m) and the symbol-common scrambling sequencer′_(l′,n) _(s) (m) are mapped to complex-valued modulation symbolsa_(k,l) ^((p)) used as reference symbols on antenna port p according tothe equation (11).

According to the present embodiment, the random seeds for thesymbol-common sequences are based on cell ID or CSI-RS ID or IM-RS ID.

According to the present embodiment, random seeds for the symbol-commonsequences and the symbol-specific sequences and the OCCs are signaled touser equipment or to be specified for each port.

According to the present embodiment, the reference signals areinterference measurement reference signals.

According to the present embodiment, by the configuration of OCC andscrambling on IM-RSs, IM-RSs from multiple LPNs are kept fullyorthogonal with IM-RSs from multiple macro nodes and quasi-orthogonalityis obtained among the multiple LPNs and among multiple macro nodes, sothat, when detecting the interference from a LPN, the interference froma macro node can be eliminated thoroughly while the interference fromother LPNs can be effectively reduced.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams, flowcharts,and/or examples. Insofar as such block diagrams, flowcharts, and/orexamples contain one or more functions and/or operations, it will beunderstood by those skilled in the art that each function and/oroperation within such block diagrams, flowcharts, or examples can beimplemented, individually and/or collectively, by a wide range ofhardware, software, firmware, or virtually any combination thereof. Inone embodiment, several portions of the subject matter described hereinmay be implemented via Application Specific Integrated Circuits (ASICs),Field Programmable Gate Arrays (FPGAs), digital signal processors(DSPs), or other integrated formats. However, those skilled in the artwill recognize that some aspects of the embodiments disclosed herein, inwhole or in part, can be equivalently implemented in integratedcircuits, as one or more computer programs running on one or morecomputers (e.g., as one or more programs running on one or more computersystems), as one or more programs running on one or more processors(e.g., as one or more programs running on one or more microprocessors),as firmware, or as virtually any combination thereof, and that designingthe circuitry and/or writing the code for the software and or firmwarewould be well within the skill of one of those skilled in the art inlight of this disclosure. In addition, those skilled in the art willappreciate that the mechanisms of the subject matter described hereinare capable of being distributed as a program product in a variety offorms, and that an illustrative embodiment of the subject matterdescribed herein applies regardless of the particular type of signalbearing medium used to actually carry out the distribution. Examples ofa signal bearing medium include, but are not limited to, the following:a recordable type medium such as a floppy disk, a hard disk drive, aCompact Disc (CD), a Digital Video Disk (DVD), a digital tape, acomputer memory, etc.; and a transmission type medium such as a digitaland/or an analog communication medium (e.g., a fiber optic cable, awaveguide, a wired communications link, a wireless communication link,etc.).

With respect to the use of substantially any plural and/or singularterms herein, those having skills in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

1. A user equipment comprising: a receiver, which, in operation,receives a plurality of channel state information-reference signals(CSI-RSs) based on one or more CSI-RS configurations; and circuitry,which, in operation, calculates a channel quality indicator (CQI) basedon the plurality of CSI-RSs, wherein two or more CSI-RS configurationsare used for more than eight CSI-RS ports, and wherein each of theplurality of CSI-RSs is generated based on a value selected from one ofa cell ID or another cell ID indicated by a higher layer signaling. 2.The user equipment according to claim 1, wherein each CSI-RS transmittedusing each CSI-RS port among the plurality of CSI-RSs is multiplied withone of a plurality of orthogonal sequences having a length of four. 3.The user equipment according to claim 1, wherein each CSI-RS transmittedusing each CSI-RS port among the plurality of CSI-RSs is multiplied withone of a plurality of orthogonal sequences having a length of four andis mapped to two orthogonal frequency-division multiplexing (OFDM)symbols and to two subcarriers.
 4. The user equipment according to claim3, wherein the two OFDM symbols are two consecutive OFDM symbol.
 5. Theuser equipment according to claim 3, wherein the two subcarriers are sixsubcarriers apart from each other in a frequency domain.
 6. The userequipment according to claim 1, wherein the plurality of CSI-RSs arereceived from a plurality of transmission points which include a macronode and one or more low power nodes (LPNs).
 7. The user equipmentaccording to claim 2, wherein the plurality of orthogonal sequenceshaving the length of four include [1, 1, 1, 1], [1, −1, 1, −1], [1, 1,−1, −1] and [1, −1, −1, 1].
 8. A communication method comprising:receiving a plurality of channel state information-reference signals(CSI-RSs) based on one or more CSI-RS configurations; and calculating achannel quality indicator (CQI) based on the plurality of CSI-RSs,wherein two or more CSI-RS configurations are used for more than eightCSI-RS ports, and wherein each of the plurality of CSI-RSs is generatedbased on a value selected from one of a cell ID or another cell IDindicated by a higher layer signaling.
 9. The communication methodaccording to claim 8, wherein each CSI-RS transmitted using each CSI-RSport among the plurality of CSI-RSs is multiplied with one of aplurality of orthogonal sequences having a length of four.
 10. Thecommunication method according to claim 8, wherein each CSI-RStransmitted using each CSI-RS port among the plurality of CSI-RSs ismultiplied with one of a plurality of orthogonal sequences having alength of four, and is mapped to two orthogonal frequency-divisionmultiplexing (OFDM) symbols and to two subcarriers.
 11. Thecommunication method according to claim 10, wherein the two OFDM symbolsare two consecutive OFDM symbol.
 12. The communication method accordingto claim 10, wherein the two subcarriers are six subcarriers apart fromeach other in a frequency domain.
 13. The communication method accordingto claim 8, wherein the plurality of CSI-RSs are received from aplurality of transmission points which include a macro node and one ormore low power nodes (LPNs).
 14. The communication method according toclaim 9, wherein the plurality of orthogonal sequences having the lengthof four include [1, 1, 1, 1], [1, −1, 1, −1], [1, 1, −1, −1] and [1, −1,−1, 1].